Institute of Novel Materials and Technology, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia

E. A. Kuzas, Associate Professor at the Department of Metallurgy of Non-ferrous Metals, Candidate of Technical Sciences, e-mail: e.kuzas@ya.ru

Laboratory of Advanced Technologies in Non-ferrous and Ferrous Metals Raw Materials Processing, Institute of Novel Materials and Technology, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia

K. A. Karimov, Senior Researcher, Candidate of Technical Sciences
D. A. Rogozhnikov, Head of the Laboratory, Doctor of Technical Sciences

Department of Rare Metals and Nanomaterials, Institute of Physics and Technology, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia

I. P. Sandalov, Engineer

Iron collector is a type of middlings produced in spent automotive catalyst recycling. Platinum group metals are encapsulated in the ferrosilicium matrix, ferrosilicium being the main component of the collector. Application of conventional hydrometallurgical processes (such as leaching in hydrochloric or sulphuric acids) for ferrosilicium liberation does not appear to be effective. So, it is proposed to use a mixture of hydrochloric and hydrofluoric acids for leaching of the collector in order to intensify the hydrometallurgical process. The said process ensures a high degree of liberation of the ferrosilicium matrix resulting in the production of cakes suitable for further refining. Using the shrinking core model, the authors of this research study examined the kinetics of leaching an iron collector containing ferrosilicium phases in a mixture of hydrochloric and hydrofluoric acids. Some generic kinetic equations were obtained as a result, which adequately describe the process of iron recovery in solution (R² = 0.96) and that of silicon recovery in gas phase (R² = 0.93) at the concentration of hydrochloric acid of 2.74 to 6.86 mol/l, that of hydrofluoric acid of 1.50 to 7.50 mol/l, at the temperature of 323 to 363 K and the iron collector leaching duration of 0 to 110 min. The concentration of hydrochloric acid and the temperature were found to produce the strongest effect on iron recovery in the case of iron recovery in solution, whereas in the case of silicon recovery in gas phase it was the concentration of hydrofluoric acid. Apparent activation energy values were calculated: 38.7 kJ/mol for iron and 4.3 kJ/mol for silicon. These values are typical of processes developing in transition and diffusion modes, respectively. Diffusion of reagents through the layer of products present at the ferrosilicium surface adsorbed (SiF₄) and in the form of conglomerates (FeF₂) was found to be the limiting stage of the iron collector leaching process. The authors defined certain iron collector leaching parameters that enable to liberate at least 95% of ferrosilicium avoiding precipitation of secondary phases.
This research was funded by the Ministry of Science and Higher Education of the Russian Federation as part of the Development Programme of the Ural Federal University named after the First President of Russia B. N. Yeltsin, in line with the Strategic Academic Leadership Programme Prioritet-2030.
Contributors to this research study include D. I. Golovkin, a Research Engineer at the Laboratory of Advanced Technologies in Non-ferrous and Ferrous Metals Raw Materials Processing, Institute of Novel Materials and Technology, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia.

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